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Therapy with T-FLEX Ankle-Exoskeleton for Motor Recovery:
A Case Study with a Stroke Survivor
Daniel Gomez-Vargas, Maria J. Pinto-Bernal, Felipe Ball´
en-Moreno,
Marcela M´
unera, Member, IEEE, and Carlos A. Cifuentes, Member, IEEE
Abstract— Stroke is the main neurological condition causing
disability worldwide. Physical therapy and robotic devices have
been used in rehabilitation to recover lost locomotor func-
tions. Despite the advantages of using robots in rehabilitation
scenarios, some joints remain with alterations after therapy
processes (e.g., the ankle joint). This paper presents a single
case study of a patient with chronic stroke who participated
in 18 sessions to assess the effects of T-FLEX in lower limb
kinematics, spatiotemporal parameters, and muscular activity.
To this end, each session consisted of two modalities: (1) 90-
degree knee flexion, and (2) complete knee extension. The
results showed improvement in the participant’s spatiotemporal
and kinematic parameters, as well as in the foot clearance
during the swing phase. Regarding the muscular activity, the
first sessions showed considerable increases related to the
patient’s inactivity. However, as the experiment proceeded, this
value decreased as a consequence of the adaptation to the
device. Regarding the electrical activity measured during each
session, both muscles (i.e., gastrocnemius and tibialis anterior)
tended to increase at the end-stage.
I. INTRODUCTION
Nowadays, Stroke is the main cause of disability and
the second leading cause of death worldwide [1]. Survivors
present both dysfunctions on the locomotor system and
cognitive alterations due to neurological damages [2]. Specif-
ically, after the episode, the subject can suffer conditions
such as severe or complete loss of motor functions (hemiple-
gia), weakness (hemiparesis) of one entire side of the body,
and tightness due to continuous contraction of the muscles
(spasticity) [3].
Conventional physical therapy has been used to recover
the lost abilities and hence improve the patients’ quality
of life [4]. Additionally, the inclusion of robotic devices
in this rehabilitation process have enhanced a higher user’s
level of recovery [5]–[7]. Those devices apply concepts of
neuroplasticity and the adaptability of the central nervous
system in their actuation control designs, which are induced
by repetitive and task-oriented therapies [8].
Despite the advantages of using robotics in rehabilitation,
some joints remain with dysfunctions. For instance, the
ankle, which is a fundamental joint in the gait cycle since it
This work was supported by Colombia Colciencias (grant 801-2017) and
Colombian School of Engineering Julio Garavito.
Daniel Gomez-Vargas, Maria J. Pinto-Bernal, Felipe Ball´
en-
Moreno, Marcela M´
unera and Carlos A. Cifuentes are
with Department of Biomedical Engineering, Colombian
School of Engineering Julio Garavito, Bogot´
a, Colombia
{daniel.gomez-v, maria.pinto, felipe.ballen}
@mail.escuelaing.edu.co, {marcela.munera,
carlos.cifuentes}@escuelaing.edu.co
allows controlled contact with the ground, the redirection of
the center of mass, and the provision of propulsive forces to
initiate the swing [9].
T-FLEX is an ankle exoskeleton based on variable stiff-
ness actuation [10]. This device includes a novel composite
tendon whose mechanical behavior is similar to the human
Achilles tendon [11]. T-FLEX assists in dorsi-plantarflexion
movements. In this sense, it has been designed to avoid
restriction of the natural movements on the ankle.
This paper reports initial results in a stroke survivor for
the therapy mode of T-FLEX. The first goal was related
to determine the appropriate exercises for this modality,
taking as a principle, the increase of muscular activity on
the affected shank. The second goal consisted in assessing
the effects of the orthosis on kinematic and spatiotemporal
parameters of the patient. Finally, the last goal intended to
analyze the effects in the spasticity of the participant after
the therapy sessions.
II. METHODOLOGY
This section describes the experimental protocol that was
designed to address the hypotheses.
A. Research Questions and Experimental Hypothesis
In concordance with the objectives of this study, the
research question and hypothesis are described below:
•Q1: Does the use of T-Flex orthosis improve the kine-
matic and spatiotemporal parameters of the patient?
•Q2: Does the use of T-Flex orthosis reduce the patient’s
spasticity level at the end of the sessions?
•H0: T-Flex orthosis does not increase the muscular
activity on the patient affected shank.
To address the above question, a study was executed at
the Colombian School of Engineering Julio Garavito, where
one volunteer with chronic hemiplegic stroke used the T-
FLEX orthosis in a rehabilitation program. The next sections
describe ethics statements, the participant’s requirements, the
experimental design, and the experimental procedure.
B. Ethics Statement
The protocol was approved by the Research Ethics Com-
mittee of the Colombian School of Engineering Julio Gar-
avito. The participant was informed about the scope and
purpose of the experiment, and his/her written consent was
obtained prior to the study. The participant was free to leave
the study when he/she decided to do so.
C. Participant
This study involved a 32-year-old female volunteer who
suffered a hemorrhagic stroke. The diagnosis of the partic-
ipant was chronic hemiplegia on the right side of the body
and ankle spasticity (i.e., 1+ in the Ashworth scale). The
participant was selected using the inclusion and exclusion
criteria shown below.
a) Inclusion Criteria: A patient with chronic stroke
who suffers some ankle dysfunction. The participant must
have a low level of spasticity on the ankle (i.e., up to level
3 in the Ashworth scale) and partial independence during
walking.
b) Exclusion Criteria: According to the experimental
setup and the system features, participants under 150 cm and
over 190 cm were not considered. Likewise, subjects with
any visual, auditory, or cognitive impairments that prevent
the correct understanding of the activity will not be part of
this study. On the other hand, the subject must not present
injuries, ulcers, and pain in the affected lower limb or the
spinal cord.
D. Experimental Design
The experimental design intended to analyze and deter-
mine the effects and impact of the ankle exoskeleton T-
FLEX on a stroke survivor. The orthosis was tested in
a rehabilitation scenario using the therapy mode, which
consists of repetitive flexion and extension movements on
the ankle. To this end, four phases were defined: pre and
post functional evaluations, the experimental procedure and
Quebec User Evaluation of Satisfaction with assistive Tech-
nology (QUEST) survey.
E. Pre and Post Functional Evaluation
One of the goals of this study was to evaluate the effect of
the orthosis on spatiotemporal and kinematic parameters. To
verify this goal, a 10-meter test was performed to determine
the subject-s normal overground speed. Afterwards, the speed
was set on a rehabilitation treadmill (NIZA RX K153D-
A-3, SportFitness, Colombia) and the subject was asked to
walk on it. The participant was equipped with a G-WALK
(BTS Bioengineering, Italy) located on L2 and inertial sensor
(Shimmer3, Shimmer, Ireland) placed on on the foot tip. The
volunteer was asked to walk for at least 120 s on the treadmill
at a zero-degree inclination. Data acquisition only started
once the self-selected speed was reached, and the treadmill
speed was stopped after all data were acquired.
A functional evaluation was also carried out by a physio-
therapist. Particularly, the Ashworth scale and the range of
motion (ROM) of the patient in different joints were assessed
(e.g., knee, ankle, hallux, among others). Table I summarizes
the assessed parameters. The initial evaluation was used as
a baseline to compare the results before the rehabilitation
sessions.
F. Experimental Procedure
To accomplish this study, 18 sessions (i.e., 3 per week)
with a standard therapy procedure based on two modalities
were executed:
First modality (20 minutes): Sitting on a chair with 90-
degree knee flexion, the volunteer’s lower limb was slightly
raised to avoid floor contact (See Figure 1a).
Second modality (20 minutes): Sitting on a chair with a full
knee extension, the volunteer’s lower limb was horizontally
raised to avoid floor contact (See Figure 1b).
Between modalities, there was a five minute rest period.
Each session carried out the same experimental conditions.
First, the participant was equipped with electrodes located
on the tibialis anterior and gastrocnemius muscles of the
paretic side. An electromyogram (EMG) sensor (Shimmer3
EMG unit, Shimmer, Ireland) running at 500 Hz acquired the
electrical activity on the muscles. After this, the researcher
installed the T-FLEX orthosis on the paretic side (See Figure
1). It is important to emphasize that after the instrumenta-
tion, the device recorded the volunteer’s maximum range of
motion, which changed for each session. This calibration
is a manual procedure, where the researcher moves the
participant’s foot to reach the maximum dorsi-plantarflexion
movements. The T-FLEX actuation system executed auto-
matically those stored values during the repetitions in passive
mobilization for both modalities.
EMG Sensors
T-FLEX Orthosis
(a) First Modality
EMG Sensors
T-FLEX Orthosis
Support System
(b) Second Modality
Fig. 1: Experimental setup postures proposed for this study.
The first posture consists of a 90-degree knee flexion. The
second posture refers to a complete knee extension.
G. Quest
To evaluate the patient’s satisfaction concerning the ankle-
foot orthosis T-FLEX a QUEST (Quebec User Evaluation
of Satisfaction with assistive Technology) survey was used.
This survey consisted of 8 questions, with a maximum score
of 5 (i.e., completely satisfied), focused on aspects such as
dimensions, ease of use, and comfort during the session. For
more details see Table II.
H. Orthosis Configuration
This study employed the ankle exoskeleton T-FLEX. The
device’s weight is 1.5 Kg, including the support system, elec-
tronic components, and two actuators (MX106T, Dynamixel,
Korea). As the power supply, T-FLEX used a 4S 14.8 V
LiPo battery. From this supply system, each motor provided
a torque value close to 4.5 Nm. In terms of operation, the
device used the therapy mode, which allows the user to train
the flexo-extension motions of the ankle joint. In this way,
the control system can vary parameters such as the frequency
between repetitions, actuation velocity, and the number of
repetitive movements.
Specifically, in this protocol, the orthosis had a repeti-
tion rate of 0.6 Hz. Moreover, the actuator worked with a
velocity of 50% of the maximum motor speed, which is
approximately 20 rpm in load condition. To complete the
time in each modality, T-FLEX achieved 370 movements
for a total amount of 740 repetitions per session. All these
parameters and controllers for the actuators were running in
the Robot Operating System framework (ROS) under Linux
architecture.
I. Data processing and acquisition
Data processing was performed offline using MATLAB
software (MathWorks, 2018b, USA) and an Asus VivoBook
S15 S510UA (IntelCore i5-8250U, CPU@1.80 GHz, Tai-
wan) running Windows 10 Home. The output EMG signals
were processed with a band-pass filter to eliminate the
atypical values and remove the noise. Then, these signals
were rectified with absolute values. Subsequently, a data
smoothing was performed using a 100 ms moving average
window. Finally, the root-mean-square (RMS) was calculated
to provide as much information as possible about the ampli-
tude of the EMG signal, since it gives a measure of the signal
power.
J. Statistical Analysis
The software SPSS (IBM-SPSS Inc, Armonk, NY, USA)
was used for the statistical analysis. First, the normal distri-
bution of all data was verified employing the Shapiro–Wilks
test. Subsequently, the ANOVA test was carried out to
find statistically significant differences among the electrical
activity of each muscle in two cases: (1) comparison between
two modalities and (2) comparison of the muscular activity
during each session.
III. RESULTS
This section presents the results of one patient diagnosed
with a chronic hemiplegic stroke who participated in this
study. The results are divided into three main parts: (1) Pre
and post functional evaluation, (2) muscular activity, and (3)
a satisfaction survey of T-FLEX use.
A. Pre and Post functional evaluation
This part includes the kinematic and spatiotemporal pa-
rameters obtained from the experimental procedure presented
in the previous section. Table I illustrates the values cor-
responding to the pre and post evaluations in terms of the
passive Range of Motion (ROM). These values show changes
in 20 of 22 measured motions on the lower limb joints,
where extension on the hallux metatarsophalangeal and prox-
imal extension on the fifth toe interphalangeal remained the
same. However, the most significant changes were related
to increases in the joint range for the movements on the
hip, dorsi-plantarflexion on the ankle, flexo-extension on
the hallux interphalangeal joint, and flexion on the fifth toe
interphalangeal joint. The other measures exhibited changes
of less than 15% in respect of the initial evaluation.
Moreover, for the kinematic results, the ankle angular
motion during the walking over treadmill followed a normal
distribution. Thus, the gait cycles were averaged to obtain a
unique curve. This curve allowed estimating the parameters
shown in Figure 2. The maximum kinematic change pre-
sented during the walking analysis was the reduction in 25%
of the extension movement on the swing phase. Additionally,
the spatiotemporal parameters showed improvement inher-
ently related to an increase in the subject’s natural walking
speed.
DF PF GC time Cadence
-25
-20
-15
-10
-5
0
5
Percentage of variation [%]
Variation of kinematic parameters with reference to the prior functional evaluation
Fig. 2: Percentage of variation for the kinematic and spa-
tiotemporal parameters in walking over the treadmill (DF:
Average values of the maximum dorsiflexion angles during
gait cycles, PF: Average values of the maximum plantarflex-
ion angles during gait cycles, GC: gait cycle). The positive
values refer to increases concerning the initial functional
evaluation. In contrast, negative values represent a reduction
in the parameter.
Furthermore, the Ashworth scale, estimated using the
functional evaluation, had a reduction in one level from 1+
to 1 after the therapy sessions.
TABLE I: Subject’s Range of Motion (ROM) on the lower limb joints for the pre and post functional evaluations. The
highlight values indicate the most relevant changes after the therapy sessions.
(a) Range of Motion on the hip and knee joints for both limbs
Initial Functional Evaluation Final Functional Evaluation
Body Part Paretic Side (deg) Healthy Side (deg) Body Part Paretic Side (deg) Healthy Side (deg)
Hip Abduction (L5,S1) 30 45 Hip Abduction (L5,S1) 45 45
Hip Adduction (L1-L4) 20 35 Hip Adduction (L1-L4) 30 35
Hip Flexion (T12-T13) 116 125 Hip Flexion (T12-T13) 122 125
Hip Extension (L5-S1) 18 25 Hip Extension (L5-S1) 20 25
Knee Flexion (L4-S1) 140 136 Knee Flexion (L4-S1) 140 136
Knee Extension (L2-L5) 10 4 Knee Extension (L2-L5) 10 4
(b) Range of Motion on the ankle and foot joints for the paretic side
Initial Functional Evaluation Final Functional Evaluation
Body Part Paretic Side (deg) Body Part (deg) Paretic Side (deg)
Ankle Plantar Flexion (S1) 15 Ankle Plantarflexion (S1) 45
Ankle Dorsi Flexion (L4,L5) 15 Ankle Dorsiflexion (L4,L5) 24
Ankle Inversion 33 Ankle Inversion 35
Ankle Eversion 22 Ankle Eversion 25
Hallux Metatarsophalangeal Flexion 43 Hallux Metatarsophalangeal Flexion 45
Hallux Metatarsophalangeal Extension 47 Hallux Metatarsophalangeal Extension 47
Fifth Finger Metatarsophalangeal Flexion 64 Fifth Finger Metatarsophalangeal Flexion 68
Fifth Finger Metatarsophalangeal Extension 60 Fifth Finger Metatarsophalangeal Extension 65
Hallux Interphalangeal Flexion 37 Hallux Interphalangeal Flexion 44
Hallux Interphalangeal Extension 0 Hallux Interphalangeal Extension 5
Fifth Toe Interphalangeal Proximal Flexion 34 Fifth Toe Interphalangeal Proximal Flexion 40
Fifth Toe Interphalangeal Proximal Extension 0 Fifth Toe Interphalangeal Proximal Extension 0
Fifth Toe Interphalangeal Distal Extension 30 Fifth Toe Interphalangeal Distal Extension 34
Fifth Toe Interphalangeal Distal Flexion 36 Fifth Toe Interphalangeal Distal Flexion 39
B. Muscular activity
The second part constitutes the muscular activity measured
on the tibialis anterior and gastrocnemius muscles during the
session. Figure 3 shows the mean RMS values per session in
each modality. On the one hand, the tibialis anterior regis-
tered a significant increase of the muscular activity up to the
third session (See Figure 3a). For the following sessions, this
value had a reduction and maintained its magnitude between
0.004 mV and 0.015 mV. Moreover, both modalities showed
similar electrical amplitudes throughout the experiment.
On the other hand, the muscular activity of the gastroc-
nemius increased up to the fourth session (See Figure 3b).
The mean RMS values after this session had a reduction
as also occurred in the tibialis anterior. In general terms,
the gastrocnemius reached a greater activation of electrical
activity in comparison with the tibialis anterior during the
first sessions. Nevertheless, this activity showed lower mean
RMS values than the other muscle from the ninth session.
Additionally, the behavior of muscular activity during the
therapy session was analyzed. To this end, it was calculated
the mean of the electrical activity on time windows with a
size of 10 seconds. The first window was used as a reference
to calculate the change in the other moments. Figure 4
illustrates this behavior throughout the session.
The tibialis anterior muscle presented variability at the
half time of the first modality. However, this muscle showed
a tendency to increase its electrical activity at the end-stage
of the sessions (See Figure 4a). The gastrocnemius muscle
showed high variability for the complete knee extension
posture taking values up to 130 % in comparison with the
first minutes. Conversely, the 90-degree knee flexion posture
had similar variation all the time, although with a slight
increase in the final part.
1) Statistical values: ANOVA tests were performed to
find statistically significant differences among the muscular
activity between modalities during the study and the electri-
cal activity progression during the session. The results are
presented below.
•Muscular activity between modalities: The electrical
activity of the tibialis anterior muscle did not show
statistically significant differences (p>0.05) during
the study. In the same way, the gastrocnemius muscle
also did show statistical differences (p>0.05) between
modalities.
•Muscular activity progression during the session:
Results related to the electrical activity progression of
the tibialis anterior muscle showed statistically signifi-
cant differences (p<0.05). Likewise. the gastrocnemius
muscular activity showed statistical differences (p<
0.05).
C. Quest
Finally, this part presents the results of the QUEST test
performed to the patient after therapy sessions (see Table
II). In general terms, the perception of the user with the
device was acceptable, emphasizing aspects such as safety
and comfort. However, other topics (i.e., adjustments, and
ease of use) presented the lowest score.
0 2 4 6 8 10 12 14 16 18
Session
0
5
10
15
20
25
30
Mean RMS (mV)
Mean RMS values from each tibialis anterior muscle session
First modality
Second Modality
(a) Tibialis anterior muscle
0 2 4 6 8 10 12 14 16 18
Session
0
10
20
30
40
50
Mean RMS (mV)
Mean RMS values from each gastrocnemius muscle session
First modality
Second Modality
(b) Gastrocnemius muscle
Fig. 3: Mean RMS values per session during the study. The
red line represents the values for the modality with 90-degree
knee flexion. The gray line refers to obtained values with a
posture of complete extension of the knee.
TABLE II: QUEST survey responses for the T-FLEX orthosis
after the therapy sessions. The values are assessed in a scale
of 0 to 5
QUEST item Level of Satisfaction
Dimensions (size, height, length,width) 4
Weight 3
Adjustments (fixing,fastening) 3
Safety (secure) 4
Ease of use 3
Comfort 4
Effectiveness 4
Device satisfaction 3.57
IV. DISCUSSION
Following the same order, this section presents the discus-
sion and analysis of the results obtained in the study. In the
first place, according to the pre and post functional evalua-
tion, the preliminary results reported significant changes in
the increment of passive ROM in different joints, such as the
ankle, hip, and the hallux interphalangeal joints. However,
regarding the other measures, there is only a slight increase
of less than 15 %. On the other hand, the greatest increase in
terms of ROM occurred in the ankle joint, specifically in the
dorsi-plantarflexion movement. These changes are related to
the reduction of the foot spasticity reflected in the Ashworth
scale measured in both evaluations.
According to the kinematic results, the preliminary results
reported an inherent improvement in spatiotemporal parame-
(a) Tibialis anterior muscle
(b) Gastrocnemius muscle
Fig. 4: Muscular activity behavior throughout the session in
respect of mean and standard deviation between sessions.
The red curve describes the behavior of the muscle in the
modality with 90-degree knee flexion. The gray curve shows
the behavior in the complete knee extension modality.
ters due to an increase in the patient’s speed. Also, it showed
a 25 % reduction in the plantarflexion movement. This value
is related to an increase in ankle dorsiflexion during the
swing phase, which indicates an enhancement in the foot
clearance for the patient in walking. The improvement of
this parameter is associated with decreases in fall risks and
ankle injuries [12]. The above suggests that effectively a
rehabilitation program with the T-FLEX orthosis helps to
improve the spatiotemporal and kinematic parameters at the
end of the entire therapy sessions. To this end, the first
research question (Q1) is answered, i.e., T-FLEX orthosis
improves the kinematic and spatiotemporal parameters of the
patient.
Regarding Ashworth scale results, it showed a reduction
in one from 1+ to 1 at the end of the entire therapy sessions.
With this, the second research question (Q2) is answered,
which means that the use of T-FLEX orthosis contributes to
the reduction of the patient’s spasticity level.
These results coincide with the changes presented by
Cheng et al., where the spatiotemporal parameters had an
increase, and the spasticity level decreased after the ses-
sions [13]. However, in contrast to this protocol, they used
electrical stimulation after the repetition exercises. Likewise,
Tamburrella et al. also presented similar results asserting that
if it is included electromyography as a control signal, the
results will be more effective in terms of spasticity and ROM
[14]. Therefore, to engage the patient with the therapy and
improve the outcomes reported in this study, the following
protocols could include both active control and feedback
strategies.
In the second place, for the muscular activity context,
the preliminary results reported an increase in electrical
activity during the first stage of the experiment. Neverthe-
less, this activity presented a decrease from the third and
fourth sessions for the tibialis anterior and gastrocnemius
muscles, respectively. These results suggest that during the
first sessions, given that the muscle comes from a period
of inactivity, any exercise performed over it induces high
values of electrical activity. However, as early as the muscle
overcame the adaptation period, the same training did not
produce enough effort to generate high electrical activity
values [15], [16]. Hence, a variable rehabilitation program
with T-FLEX orthosis, where the requirement and the effort
increase over time, could provide better results.
Concerning the muscular activity in the session, the results
showed an increase in the electrical values at the end-stage
for both muscles. This also can be seen in the statistical
results, since it did not report statistically significant differ-
ences. Therefore, the null hypothesis is rejected (Ho), and it
can be inferred that the use of TFLEX orthosis increases
the muscular activity on the patient during each session.
Nevertheless, it should be emphasized of high variability
between sessions illustrated in Figure 4. This variability is
mainly noted for the second modality of the gastrocnemius
and the first modality of the tibialis anterior muscle. The
variability can be related to the decrease of the muscular
activity after the adaptation period, where the electrical
activity showed minimum increases.
Another aspect analyzed was the difference between the
modalities proposed in this study. Nevertheless, the statistical
results suggest that the modalities do not affect the electrical
activity in the measured muscles.
Finally, the patient perception with the use of T-FLEX in
the rehabilitation program was positive. The most important
aspects highlighted by the user were safety, comfort, and
effectiveness. Although other characteristics such as weight,
ease of use, and adjustments, should be taken into consider-
ation in subsequent studies.
V. CONCLUSIONS AND FUTURE WORKS
This paper presented the obtained results from a single
case of study for the therapy mode with the T-FLEX orthosis.
The study showed improvement in kinematic and spatiotem-
poral parameters on a chronic stroke patient. Moreover,
the participant exhibited a spasticity reduction according to
the Ashworth scale. On the other hand, muscular activity
increased its value during the first sessions, although this
value had a reduction probably related to adaptation issues.
Moreover, the measured muscles showed increases in their
electrical activity at the end-stage of each session, though
they presented high variability between sessions. Finally, the
patient’s perception in the use of T-FLEX for rehabilitation
programs was positive.
Future works should focus on the recruitment of ad-
ditional pathological subjects to validate the efficacy of
the therapeutic modality of T-FLEX in a larger sample of
patients. Additionally, it should be proposed a novel protocol
where the patient has different levels of effort and feedback
strategies, allowing the improvement of these results.
ACKNOWLEDGMENT
The authors would like to especially thank the patient
that participated in this study and contributed with her
feedback and experience in the improvement of the device.
Also, we want to recognize the support of the Center for
Biomechatronics team in the execution of this experiment.
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